Novel membrane electrode assembly (MEA) architecture for improved durability for a PEM fuel cell

ABSTRACT

An electrically conductive fluid distribution element for use in a fuel cell having a layer of a conductive non-metallic fiberless microporous media. In certain embodiments, an electrically conductive metal is deposited along a surface of the element to form one or more metallized regions. The metallized regions are arranged to contact a membrane electrode assembly (MEA) in a fuel cell assembly, and thus improve electrical conductance at contact regions between the MEA and the layer of media. Methods of making such a fluid distribution element and operating fuel cell assemblies are also provided.

FIELD OF THE INVENTION

The present invention relates to electrochemical cells, and moreparticularly to electrically conductive fluid distribution elements andthe manufacture and operation of fuel cells incorporating such fluiddistribution elements.

BACKGROUND OF THE INVENTION

Fuel cells have been proposed as a power source for electric vehiclesand other applications. One known fuel cell is the PEM (i.e., ProtonExchange Membrane) fuel cell that includes a so-called “membraneelectrode assembly” (MEA) comprising a thin, solid polymermembrane-electrolyte having an anode on one face of themembrane-electrolyte and a cathode on the opposite face of themembrane-electrolyte. A polymer selected for use as a PEM desirably hasunique characteristics including permeability to protons and electricalinsulation. In practice, polymers that fulfill these requirements tendto be relatively fragile and thin, with a typical thickness ofapproximately 10 to 125 μm. When adding the electrodes to the PEM toform the MEA, the PEM is subjected to relatively high stress conditionsincluding both high temperature and pressure. Since the PEM membrane isfragile, it is handled and processed carefully to minimize physicaltears or thinning.

The MEA is sandwiched between a pair of electrically conductive porousfluid distribution media layers. The MEA together with the fluiddistribution elements form a compliant layer, which is then sandwichedbetween a pair of electrically conductive contact elements (generallycalled bipolar or separator plates) that serve as current collectors forthe anode and cathode, and further often contain appropriate channelsand openings for distributing the fuel cell's gaseous reactants (i.e.,H₂ & O₂/air) over the surfaces of the respective anode and cathode.

Diffusion media are typically made from fibers (preferably carbon orgraphite fibers) or metals, such as foams or screens. Such diffusionmedia generally has the potential for manufacturing flaws, includingsmall protrusions (such as protruding fibers) that may potentially causedamage to the MEA. Further, separator plate contact with adjacentelements is achieved by the application of compressive force, and mustbe optimized to enhance fuel cell operation without causing damage tothe MEA. Overall, the associated components and assembly contacting theMEA can lead to excessive wear and strain, shortening the lifespan ofthe fuel cell. There is a need for a protective layer to cushion theMEA, while not detracting from electrical performance of the fuel cell,nor adding excessive cost to the fabrication of the fuel cell. Thereremains the challenge to optimize fuel cells, including the diffusionmedia elements and assemblies made therefrom in a fuel cell to promoteefficiency, electrical conductivity, and MEA durability ascost-effectively as possible.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to a fluid distributionelement for a fuel cell having a membrane electrode assembly (MEA). Theelement comprises a layer comprising electrically conductive fiberlessmicroporous distribution media. A surface of the layer has one or moremetallized regions. The one or more metallized regions contact a majorsurface of the MEA and form respective electrically conductive pathsbetween the MEA and the media.

Another aspect of the present invention relates to a method of operatinga fuel cell comprising positioning an electrically conductive fiberlessmicroporous distribution media between a membrane electrode assembly(MEA) and an electrically conductive substrate. The microporous mediahas a first surface confronting the MEA and a second surface confrontingthe conductive substrate. The one or more regions of the first surfaceare contacted with the MEA and the one or more regions of the secondsurface are contacted with the substrate to form an electricallyconductive path from the substrate through the microporous media to theMEA. Electrons are then conducted to or from the MEA via theelectrically conductive path while operating the fuel cell.

In another aspect, the present invention provides a method formanufacturing an assembly for a fuel cell, comprising depositing anelectrically conductive metal on a surface of an electrically conductivefiberless microporous media to form one or more metallized regionshaving an ultra-thin thickness. The microporous media comprisescarbonized expanded-polytetrafluroethylene (ePTFE). The surface havingthe metallized regions is positioned adjacent to an electrode of amembrane electrode assembly (MEA). The electrode is contacted with thesurface having the metallized regions to form an electrically conductivepath between the substrate and the microporous media.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a not-to-scale side-sectional view of a fuel cell assemblyhaving an membrane electrode assembly (MEA), fiberless microporouselectrically conductive fluid distribution media with metallized regionsapplied to a surface thereof in accordance with the present invention,where the assembly also comprises separator elements;

FIG. 2 is an exploded view of a section of FIG. 1 showing anelectrically conductive fiberless microporous fluid distributionelement;

FIG. 3 is a not-to-scale side-sectional view of an alternate embodimentaccording to the present invention comprising metallized regions alongthe entire surface of a layer of microporous fluid distribution mediafacing an MEA and having metallized regions along an entire surface ofmicroporous media facing separator plates;

FIG. 4 is a not-to-scale partial side-sectional detailed view of asingle layer of fiberless microporous media adjacent to an MEA accordingto an alternate preferred embodiment of the present invention havingmetallized regions along the entire surface of the layer of microporousmedia facing an MEA and along a surface of microporous media facingseparator plates where the metallized regions are discrete; and

FIG. 5 is a graph of contact resistance and voltage values achieved byan electrically conductive fiberless microporous fluid distributionmedia element according to the present invention, wherein the relativehumidity of the cathode inlet is varied to demonstrate overall cellperformance.

DETAILED DESCRIPTION

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. The headings and sub-headings used herein areintended only for general organization of topics within the disclosureof the invention, and are not intended to limit the disclosure of theinvention or any aspect thereof. Subject matter disclosed in the“Summary of the Invention” is not an exhaustive or complete disclosureof the entire scope of the invention or any embodiments thereof.

DEFINITIONS

As used herein, the words “preferred” and “preferably” refer toembodiments of the invention that afford certain benefits, under certaincircumstances. However, other embodiments may also be preferred, underthe same or other circumstances. Furthermore, the recitation of one ormore preferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

As used herein, the word “include,” and its variants, is intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that may also be useful in the materials,compositions, devices, and methods of this invention.

As referred to herein, all compositional percentages are by weight ofthe total composition, unless otherwise specified.

As referred to herein, the word “substantially,” when applied to acharacteristic or property of a composition or method of this invention,indicates that there may be variation in the characteristic withouthaving substantial effect on the chemical or physical attributes of thecomposition or method.

“Substantially free” is intended to mean that the property orcharacteristic is absent to the extent that it cannot be detected or itis still suitable to use the item for its intended purpose where theabsence of the desired characteristic or property is required.

“About” when applied to values indicates that the calculation or themeasurement allows some slight imprecision in the value (e.g., with someapproach to exactness in the value; approximately or reasonably close tothe value; nearly). If, for some reason, the imprecision provided by“about” is not otherwise understood in the art with this ordinarymeaning, then “about” as used herein indicates a possible variation ofup to 5% in the value.

As used herein, “major surface” refers to a surface of an element havinga greater dimension or surface area than other surfaces of the element,for example, an element that has an aspect ratio of greater width toheight, where the surface area of the side corresponding to theelement's height (e.g., thickness) is significantly smaller than thesurface area of the width of the same element.

“Compliant” is a characteristic indicating that a material hasflexibility in at least one axial direction.

The term “fiberless” means a material is substantially free of elongatedparticles having an evident long axis with respect to which the particlebody is symmetrical. Examples of elongated particles having an evidentlong axis, include, fibers, fibrils or filaments, or mixtures thereof,for example.

Unless otherwise indicated, “pore size” refers to an average or medianvalue including both the internal and external pore diameter sizes. Theterms “pore” and “pores” refers to pores of various sizes, includingso-called “macropores” (pore size greater than 50 nanometers (nm)diameter), “mesopores” (pore sizes having diameter between 2 nm and 50nm), and “micropores” (pore sizes less than about 2 nm or 20 Angstromdiameter). “Microporous” indicates that a majority of the pores in thematerial have pore sizes of less than about 2 nm.

“Ultra-thin” refers to thicknesses less than about 40 nm, and mostpreferably less than 15 nm.

Fuel Cell

The present invention relates to an improved fluid distribution mediaelement for use in a fuel cell. The fluid distribution media elementincorporated into a fuel cell assembly improves aspects of fuel celloperation, including: improved performance, electrical conductivity,efficiency, and durability.

One embodiment of an exemplary fuel cell assembly is shown in theFIG. 1. A fuel cell 9 comprises a membrane-electrode-assembly (MEA) 10.The MEA 10 comprises a proton exchange membrane (PEM) 12 sandwichedbetween two electrodes 13. One electrode is an anode 14 and the oppositeelectrode is a cathode 16, which are respectively bounded byelectrically-conductive material known as porous “diffusion media”elements or layers 17 which distribute reactant gases to the MEA 10.Oxygen reactant is delivered to the cathode 16 and hydrogen reactant isdelivered to the anode 14. Protons generated at the anode 14 migratethrough the MEA 10 to the cathode 16 via the proton exchange membrane12. Water is generated as a byproduct at the cathode 16 via the reactionof the protons with oxygen. In a simplified single fuel cell, theelectrons released at the anode 14 are conducted through an externalcircuit (not shown) connected to the cathode 16 to generate electricalcurrent.

Proton Exchange Membrane

The proton exchange membrane (PEM) 12 is a solid polymeric protonconductive recast ionomer membrane that transports H⁺ ions. One broadclass of cation exchange proton conductive resins well known in the artis the so-called sulfonic acid cation exchange resin, such as those soldunder the trade name Nafion® sold by E.I. DuPont de Nemours & Co. Othersimilar membranes are sold by Asahi Glass and Asahi Chemical Company.The electrodes 13 are preferably well adhered to membrane 12 and provideproton transfer by intimate contact between each electrode 14,16 and theionomer membrane 12.

Electrodes

As best shown in FIG. 2, a detailed view of a portion of FIG. 1, each ofthe electrodes 13 are formed of a corresponding group of finely dividedelectrically conductive carbon particles 18 supporting very finelydivided electrically conductive catalytic particles 19. Proton (cation)conductive material 20 is intermingled with the carbon and catalyticparticles 18, 19 to provide a continuous H⁺ path to the catalyst 19 forreaction. The carbon particles 18 forming the anode 14 (FIG. 1) maydiffer from those forming the cathode 16 (FIG. 1). In addition, thecatalyst 19 composition and/or loading at the anode 14 may differ fromthe catalyst 19 loading at the cathode 16. Although the characteristicsand loading of the carbon particles 18 and the catalyst 19 may differfor anode 14 and cathode 16, the basic structure of the two electrodes13 is otherwise generally similar.

One factor in catalyst 19 activity of the electrode 13 is the efficienttransfer of electrons to the catalyst 19 (in addition to oxygen andproton transport). Hence, in one aspect, the present invention providesreduced contact resistance between the fluid distribution layer 17 andthe conductive particles 18 of the electrode 13, which thus translatesto improved catalyst activity by improved electron transfer to thecatalyst particles 19.

Fluid Distribution Media

With renewed reference to FIG. 1, two fluid distribution media layers 17flank each side of the MEA 10. A first fluid distribution media layer 21confronts the anode 14, and a second fluid distribution media layer 22confronts the cathode 16. The first fluid distribution media layer 21comprises a first surface 24 and an opposing second surface 26. Thefirst surface 24 of the first media layer 21 confronts and preferablycontacts the anode electrode 14. The second fluid distribution medialayer 22 likewise comprises a third surface 28 and an opposing fourthsurface 30. The third surface 28 of the second media layer 22 confrontsand preferably contacts the cathode 16. One or more electrical contactregions 29 are formed where the fluid distribution layers 17 contact therespective electrodes 13.

Generally speaking, the porous media layers 17 serve to (1) distributegaseous reactant over the entire face of the MEA 10 (2) collect currentfrom the MEA 10 and (3) structurally support the MEA 10. Reactant fluidsare delivered to the MEA 10 via the fluid flow channels within the firstand second porous media layers 21,22, where the electrochemicalreactions occur and generate electrical current.

Separator Plate

Each porous media layer 21,22 is bounded by a current collector bipolaror separator plate (32 or 34) along the second and fourth surfaces26,30, respectively. When the fuel cell 9 is assembled, the firstseparator plate 32 surface 38 contacts a second surface 26 of the firstfluid distribution media layer 21 and a second separator plate 34surface 40 contacts the fourth surface 30 of the second fluiddistribution media layer 22. It is preferred that the fluid distributionmedia 17 and the first and second separator plates 32,34 are constructedof electrically conductive materials and that electrical contact isestablished therebetween at one or more electrical contact regions 44where an electrically conductive path is formed between a substratesheet (32 or 34) and the corresponding porous media (21 or 22). Further,it is preferred that the electrical conductivity is likewise establishedthrough the bulk of the porous media 17 and through the electricalcontact regions 29 to the electrodes 13.

Each surface 38, 40 has a flow field that is defined by a plurality oflands 48 which define therebetween a plurality of grooves 50. The fuelcell's reactant gases (i.e., H₂ or O₂) flow through the grooves and aredistributed to the MEA 10. When the fuel cell is fully assembled andcompressive force is applied, the lands 48 press against the porousmedia layers 21,22 which, in turn, press against the MEA 10.

First external surfaces 60 of the fluid distribution media 17 refers tothose surfaces (i.e., surfaces 26,30) of the first and second fluiddistribution media layers 21,22 which contact the substrate elementsheets 32,34. Second external surfaces 62 (i.e., 24,28) of the fluiddistribution media 21,22 are exposed to major surfaces 64 of the MEA 10.

Preferred materials of construction for the separator plate substrates32,34 include conductive metals, such as stainless steel, aluminum, andtitanium, for example. In certain embodiments, the separator element32,34 material forms metal oxides when subjected to oxygen. Somesuitable materials of construction for the separator plate substrates32,34 are higher grades of stainless steel that exhibit high resistanceto corrosion in the fuel cell, such as, for example, 316L, 317L, 256SMO, Carpenter 20, Inconel 601, Alloy 276, and Alloy 904L.

The several components depicted in FIG. 1 and described above aregenerally assembled together with other fuel cells to form a stack (notshown). During normal operations a fuel cell stack is operated undercompressive force creating intimate contact between the severalcomponents. Presently, this external compressive force ranges from about25 to about 600 psi (approximately 170 kPa to about 4200 kPa). However,as appreciated by one of skill in the art, the pressure may vary fromthis range and still will be equally applicable to the presentinvention.

Typical diffusion media currently used in the art is porous with about70%-90% voids, and generally is constructed carbon or graphite fibers,and is generally in the form of paper or cloth. Other types of diffusionmedia known in the art are constructed of metals, such as noble metalmesh screen. One such commonly used commercially available diffusionmedia is a graphite-fiber paper made by Toray Carbon Fibers America,Inc. However, many of the conductive diffusion media papers or clothshave rough surfaces with protrusions extending therefrom, primarily dueto the nature and structure of the fiber based material andmanufacturing processes associated therewith. While these materials aresomewhat flexible, they are not generally capable of substantialcompression or significant compliant deformation. Such diffusion mediahave the potential to cause wear and tear on the MEA 10 and shorten itslifespan. Additionally, protrusions from the fiber-based diffusion mediamay impinge on the MEA 10 and/or PEM 12 and become imbedded whenpressure is applied during fuel cell operations. The diffusion mediaprotrusions conduct electricity and may be long enough to partially orfully penetrate the membrane 12, creating potential electrical defectsin the fuel cell 9 requiring complete replacement. Hence, there havebeen some efforts to add a conductive compliant microporous bufferinglayer between the diffusion media 17 and the MEA 10, such ascommercially available CARBEL products available from W. L. GoreCompany.

However, inclusion of such a layer can add significant electricalresistance, as well as additional expense in fabricating a fuel cell.Previously heretofore, it has not been contemplated to eliminate thetraditional fiber-based electrically conductive diffusion media from thefuel cell assembly. However, the present invention eliminates the needfor such a fiber-based diffusion media, by providing a fiberlesscompliant microporous fluid distribution media having sufficientelectrical conductivity to be used in lieu of traditional fiber-baseddiffusion media.

Electrically Conductive Fiberless Fluid Distribution Media

In preferred embodiments of the present invention, the fluiddistribution media 17 comprises an electrically conductive fiberlessmicroporous media (with renewed general reference to FIGS. 1 and 2). Itis also preferred that the distribution media 17 is compliant andpreferably is capable of elastic deformation in at least two directions,so that it is axially compliant and can also be compressed, as will bedescribed below. Preferred embodiments of the media layer are“microporous” meaning that a majority of the pores in the fluiddistribution media layer 17 have pore sizes of less than about 2 nm.Since these openings are disposed internally within the body 78 of fluiddistribution media layers 17 (e.g., 21,22) the surfaces of the openingsare referred to as internal surfaces 86, or the media interior. It ispreferred that the fluid distribution media 17 is highly porous (i.e.about 60%-80% pores) having a plurality of pores 76, preferablymicropores, formed within a body 78 of the fluid distribution media 17.The plurality of pores 76 comprise a plurality of internal pores 80 andexternal pores 82 that are open to one another and form continuous flowpaths or channels 84 throughout the body 78 that extend from a firstexternal surface 60 to the second external surface 62 of the fluiddistribution media 17. Internal pores 80 are located within the bulk orbody 78 of the fluid distribution media 17 and external pores 82 end atthe distribution media layer 17 surfaces, for example, 60 or 62.

Thus, preferred fluid distribution media 17 is non-metallic electricallyconductive fiberless material that comprises a porous polymer. In oneembodiment, the material of the media layer 17 comprisespolytetrafluoroethylene (PTFE) or derivatives thereof, and further hasconductive particles distributed therein to impart electricalconductivity to the material. PTFE is also known as Teflon®. Asappreciated by one of skill in the art, the loading of conductiveparticles in the polymer is dependent upon the necessary electricalconductivity, balanced with the necessary diffusion and gas permeabilityneeded through the porous structure, as the conductive particlesgenerally occlude the pores that they occupy. It is preferred that theconductive particles have a non-fibrous geometry that does not have anevident long axis with respect to which the particle body issymmetrical, in essence a spherical shape.

Expanded polytetrafluoroethylene (ePTFE) and its microporous propertiesand characteristics are described in U.S. Pat. No. 3,953,566, that isincorporated by reference in its entirety. Desirable characteristics ofePTFE include a structure in which nodes are connected by fibrils. Othermicroporous materials include any woven or non-woven, microporousmaterials which are substantially fiberless. This includes materialssuch as conductive carbon coated on fiberless polymeric mesh or carboncloth with no z direction fibers. The microporous substrate ispreferably selected to maintain its integrity at temperatures up toabout 200° C.

Preferably, the conductive particles used are carbon particles, andtogether the ePTFE combined with the carbon particles forms “carbonizedePTFE.” The carbon particles have an average pore size (radius) in therange of about 50 to about 200 Angstroms (A). The average pore size isachieved by ball-milling which produces a suitable distribution of poresizes and relatively random distribution of equivalent particlespherical diameters. Desirably, each carbon particle has an equivalentaverage spherical diameter less than about 35 nm, and in a range ofabout 25 to about 35 nm. Examples of suitable spherical carbon particlesinclude those obtained from Cabot Corp. and sold under the name of“Vulcan XC-72R.” The Vulcan XC-72R carbon particles are ball-milled toenhance their properties. The carbon particles can also be obtained fromNoury Chemical Corp., and sold under the name of “Ketjen black.” TheKetjen black particles are used in an as-received condition.

A particularly preferred distribution media layer 17 material comprisesan expanded polytetrafluroethylene (ePTFE) having conductive carbonparticles distributed within the body, or a “carbonized ePTFE.” In oneembodiment, the ePTFE starting material has approximately 70-80% byvolume pores and 20-30% PTFE. Then, the “carbonized ePTFE” is formed byimpregnating the microporous ePTFE with a plurality of conductive carbonparticles, generally by casting a solvent slurry of a low boiling pointsolvent containing the carbon particles. The ePTFE is exposed to theslurry (preferably by immersion or dipping), however, it is not fullyimbibed, so as to leave a predetermined portion of the pores free ofcarbon particles for maintaining permeability for reactant gasdiffusion. In alternate embodiments, a matrix of conductive particlesand PTFE can be formed, and then the expansion process can be applied tocreate the desired porosity.

One such known carbonized ePTFE that is preferred as a fiberlessmicroporous fluid distribution media 17 comprises approximately 70% byvolume pores, has an uncompressed thickness of about 2.5 mils (orapproximately 65 μm) which is commercially available from the W. L. GoreCompany under the trade name CARBEL mp30z. Another electricallyconductive fiberless compliant fluid distribution media 17 preferred forcertain embodiments of the present invention comprises carbonized ePTFEhaving approximately 70% by volume pores, an uncompressed thickness ofabout 5 mils or approximately 130 μm is also sold by W. L. Gore Companyas the product CARBEL 300.

Treatment of Fluid Distribution Layers

The present invention provides a reduced electrical resistance (i.e.,increased electrical conductivity and hence increased electron transfer)from the interface of the electrode major surface 64 to the microporousfluid distribution media layer 17 surface 62 as compared to anelectrical resistance of a comparative microporous media constructed ofthe same material but having non-metallized electrical contact regionswith a similar MEA. In alternate preferred embodiments, the presentinvention further provides an overall reduction in the electricalresistance of the fuel cell assembly, by reducing the overall electricalresistance of the several assembled components of the fuel cell 9 viareduced resistance at interfaces with both surfaces 60,62 of the fluiddistribution media layers 17 confronting the MEA 10 and separatorelement substrates 32,34, respectively.

In accordance with one embodiment of the present invention, a conductivemetal is coated on the outer surfaces 81 of the pores 76 of themicroporous fluid distribution media 17 to form one or more metallizedregions 88. Applying metallized regions 88 to distribution media 17 isgenerally taught in co-pending and commonly assigned U.S. patentapplication Ser. No. 10/850,550 filed on May 20, 2004, which is hereinincorporated by reference in its entirety. The metallized regions 88 areformed along the second external surfaces 62 of the microporous medialayer 17 that confront the major surfaces 64 of the MEA electrodes 13.The metallized regions 88 integrated with the microporous fluiddistribution media layer 17 at the second external surface 62 have beendemonstrated to sustainedly reduce contact resistance when compared withcomparable microporous fluid distribution media layers having no metalcoating or metallized regions. It is preferred that the contactresistance at the interface of the electrodes 13 with the metallizedregions 88 of electrically conductive microporous fluid distributionelement 17 of the present invention is less than 30 mOhm.cm² and morepreferably less than 15 mOhm.cm². Although not limiting to the manner inwhich the present operation operates, it is believed that the conductivemetallized regions 88 at the contact surface 62 of the microporous fluiddistribution media 17 provide an improved electrical interface at thecontact regions 29 by providing a more electrically conductive interface(via the metallized regions 88) and further may be impacted bycontacting more similar materials (i.e. catalyst metals 19) withcorrespondingly similar molecular and physical characteristics (e.g.surface energies). Thus, the present invention provides enhancedelectrical conductivity, and consequently permits the use of a fiberlessmicroporous material as the fluid distribution media 17 and further mayallow for the ability to lower catalyst 19 loading in the electrodes 13by such improved electrical conductivity, hence reducing fabricationcost for the fuel cell assembly 9.

In one preferred embodiment according to the present invention, the oneor more metallized regions 88 are ultra-thin and applied along thesecond external surface 62 of the fluid distribution media 17.“Ultra-thin” layers of conductive metal deposited within the metallizedregions 88 refers to thicknesses less than about 40 nm, and mostpreferably less than 15 nm. The thickness of the metallized regions 88is preferably less than about 10 nm, more preferably from between about2 to about 10 nm, and most preferably between about 5 to about 10 nmalong the surface 62 adjacent to the electrodes 13 of the MEA 10. It hasbeen found experimentally that optimal water management (wheresufficient water is retained to permit humidification of the membrane12, while not flooding the electrodes 13) corresponds in certainembodiments to those where the thickness of the metallized region 88 onmicroporous media layers 17 along the cathode side 16 of the MEA 10 isbetween about 5 to about 10 nm, as will be described in more detailbelow.

It is preferred that the metallized regions 88 are electricallyconductive, oxidation resistant, and acid-resistant and in certainpreferred embodiments the electrically conductive metal forming themetallized region comprises a compound containing a noble metal,selected from the group consisting of: ruthenium (Ru), rhodium (Rh),palladium (Pd), silver (Ag), iridium (Ir), platinum (Pt), osmium (Os),and mixtures thereof. Such compounds may comprise elemental forms of theconductive metal, or may comprise conductive compounds of metalnitrides, metal oxides, and metal carbides. Other preferred metals forthe metallized regions 88 include those that comprise chromium (Cr),titanium (Ti), or tin (Sn). Electrically conductive compounds comprisingsuch metals include, by way of example, chromium nitride (CrN),doped-tin oxide (SnO), and doped titanium oxide (TiO). A most preferredconductive metal for the metallized regions 88 comprises gold (Au). Asrecognized by one of skill in the art, the conductive metal compositionmay comprise mixtures of the above identified metals or distinctmetallized regions 88 having different metal compositions.

In the embodiment shown in FIG. 1, both the first and second fluiddistribution layers 21,22 comprise metallized regions 88 on the surfacesfacing the MEA 10. However, while not shown, but as appreciated by oneof skill in the art, alternate preferred embodiments of the presentinvention apply to a fuel cell assembly 9 having metallized regions 88on only one of the first or second fluid distribution layer surfaces24,28 facing the MEA 10, rather than being applied to both the first andsecond fluid distribution layers 21,22, as shown.

FIG. 3 shows an alternate preferred embodiment of the present invention.Many aspects of the fuel cell assembly 11 are the same as the previousembodiment shown in FIG. 1. The second surfaces 62 of the fluiddistribution microporous media layer 17 preferably comprise the samemetallized regions 88 as described above to reduce the electricalresistance at the contact regions 29 between the microporous media layer17 and the electrodes 13. However, in the present embodiment, the firstexternal surface 60, which is the side opposite to the second surface 62of the microporous media layer 17, is additionally coated with aconductive metal to form one or more metallized regions 90. Themetallized regions 90 of the surfaces 26, 30 of respective microporousmedia layers 21, 22 preferably contact the metal substrates 32,34 toform the electrical contact regions 44. It is believed that themetallized regions 88,90, and most particularly 90, on the microporousfluid distribution media 17 provide more even electrical currentdistribution through the body 78 of the media 17 as the currentapproaches the discrete and non-continuous contact regions 44 associatedwith the lands 48 of the flow field configuration on the separator platesubstrates 32,34.

In an alternate preferred embodiment, where the first external surface60 comprises metallized regions 90, it is preferred that the thicknessof the metallized regions is less than 80 nm, preferably less than 50nm, and most preferably between about 2 to about 10 nm. In certainpreferred embodiments of the present invention, the thickness of themetallized regions 90 is less than or equal to the depth of two atomicmonolayers of the metal selected for the coating 90. The thicknesses ofthe respective metallized regions 88,90 may differ depending on theapplication, and desired thicknesses are related to both electricalconductivity and desired fuel cell operating conditions, including watermanagement. However, the electrically conductive metal of the metallizedregions 90 is preferably selected from the same compositions describedabove for the metallized regions 88. Likewise, the conductive metals ofmetallized regions 88 and 90 may be independently selected from oneanother, or may comprise the same composition, including the sameelectrically conductive metal(s). It is preferred that the conductivemetallized regions 88,90 coat the external pore 82 outer surfaces 81 andthe surfaces 86 of the internal pores 80 and extends into the body 78 ofthe fluid distribution media 17 at a depth of at least about 2 to about10 nm from respective surfaces 60 or 62.

FIG. 4 shows another preferred embodiment of the present invention,depicting the MEA 10 and one-half of the fuel cell assembly 101. Asappreciated by a skilled artisan, the present embodiment may also beemployed along both sides of the MEA 10 to form the fuel cell assembly101. The MEA 10 comprises the same elements as described in previousembodiments, including two electrodes 13 and a membrane 12. The fluiddistribution media 17 a comprises a first surface 60 a and a secondsurface 62. The second surface 62 facing the major surface 64 of the MEA10 has metallized regions 88 preferably at electrical contact regions29, formed in the same manner as previous embodiments.

The second surface 60 a of the fluid distribution media 17 a comprisesdiscrete metallized regions 90 a of the microporous media 17 whichcorrespond to electrically conductive contact regions 44 of the externalsurface 60 a, and the non-metallized regions 94 correspond to theelectrically non-conductive regions. Electrically conductive metallizedregions 90 a include those areas that contact lands 48 and establish theelectrically conductive path at the contact regions 44. In previouslydescribed embodiments, such as that in FIG. 3, the metallized regions 90entirely cover the continuous external surface 60 which promotes moreeven current distribution into the body 78 of the microporous media 17.In the embodiment of FIG. 4 with discrete metallized regions 90 acorresponding to electrically active contact regions 44, theelectrically non-conductive and non-metallized regions 94 of externalsurfaces 60 a are covered or masked while the conductive metal of themetallized regions 90 a is applied. A mask is any material that isapplied to a substrate and remains stable during coating application.Often, mask materials are selected to permit recovery and recycling ofthe metals deposited over the mask during the deposition process, andare well known in the art. Preferred mask materials compatible with thepresent invention include, by way of example, metals, such as stainlesssteel and titanium, or silicon and alumina based ceramics.

One advantage of the present invention relates to water management ofthe fuel cell. Typically, product water is generated in the fuel cellreaction and rejected at the cathode 16 where the water typicallyescapes by simple flow or by evaporation. However, means may be providedif desired, for collecting the water as it is formed to carry it awayfrom the fuel cell 9. Good water management enables successful long-termoperation of electrochemical fuel cell 9. Spatial variations of watercontent within the membrane 12 of a current-carrying fuel cell resultfrom the electro-osmotic dragging of water with proton (H⁺) transportfrom anode 14 to cathode 16, the production of water by the oxygenreduction reaction at the cathode 16, humidification conditions of theinlet gas stream, and “back-diffusion” of water from cathode 16 to anode14. Further, for currently employed PEM membranes 12, the optimalefficiency of the fuel cell occurs where the outlet humidity from thecathode is 100% relative humidity or greater. Previously, to achievethis humidity, both the anode 14 and cathode 16 reactant streams wereexternally humidified prior to entering the fuel cell 9, whichnecessitated humidification equipment. Maintaining sufficient watercontent in the fuel cell to prevent drying of the membrane has typicallybeen a significant problem during operations, thus, the inlet streams toboth the anode and cathode are humidified, usually to a target of atleast 100%.

One advantage of the present invention relates to eliminating and/orreducing the need for external humidification of the cathode 16 and/oranode 14 inlet stream. It has been discovered that where the fiberlessmicroporous sample (e.g., CARBEL fluid distribution media) was preparedwith metallized regions along both sides and used in a fuel cell thatwas operated to have a typical inlet humidity to the cathode of 100%relative humidity (which is a standard target for cathode inlethumidity), the fuel cell was inundated with excess water and in somecircumstances flooded. Thus, in contravention to known prior art, thepresent invention reduces the need for external humidification of inletreactant streams to the MEA and provides sustained membrane durabilityby providing consistent MEA humidification.

Methods

One embodiment of the present invention provides a method formanufacturing an assembly for a fuel cell, comprising depositing anelectrically conductive metal on a surface of an electrically conductivefiberless microporous media to form one or more metallized regionshaving an ultra-thin thickness, wherein the microporous media comprisescarbonized expanded-polytetrafluroethylene (ePTFE). The surface havingthe metallized regions is positioned adjacent to an electrode of amembrane electrode assembly (MEA). The electrode is later contacted withthe surface having the metallized regions to form an electricallyconductive path between the substrate and the microporous media.

A variety of depositing methods may be employed to apply the conductivemetal compositions that form the metallized regions (e.g., 88, 90, 90 a)of the fluid distribution media 17. One preferred method of depositingthe conductive metal of the metallized regions 88,90 onto the fluiddistribution microporous media 17 is by an ion-assisted, physical vapordeposition (PVD) method, which is well known in the art and described indepth in co-pending and commonly assigned U.S. patent application Ser.No. 10/850,550 filed on May 20, 2004, as previously discussed. Noblemetals are generally deposited on the substrate by the ion-assisted PVDat a rate of 0.10 nm/s to a thickness of less than 80 nm, which isobserved by thickness monitors known in the art. The metallized regions88, 90, 90 a may have conductive metal deposited onto the substrate atultra-low thicknesses of less than 80 nm, preferably less 40 nm, andmost preferably about 2 to about 10 nm. When the metallized region 88,90has a thickness of at least about 2 nm, it is preferably that theloading is 0.02 mg/cm². The use of ion-assisted, PVD apparatus allowsthe electrically conductive metal to be deposited on the substrate verysmoothly, evenly, and in an ultra-thin layer on the order of 2 to 20 nm,thereby achieving relatively uniform and good surface coverage, and goodadhesion.

Another preferred PVD method that is also suitable for the applicationof ultra-thin conductive metals is magnetron sputtering or electron beamevaporation. Other preferred methods of applying a metal coating (88,90, 90 a) according to the present invention include electroplating(e.g. electrolytic deposition), electroless plating, chemical vapor orpulse laser deposition.

Preferred embodiments of the present invention provide a low contactresistance across the separator plate substrates 32,34 through themicroporous media 17 having the metallized regions 88, 90, 90 a to theelectrodes 13 of the MEA 10. It is preferred that the contact resistanceacross an entire fuel cell (from separator plate to separator plate) isless than 100 mOhm.cm² (mΩ.cm²) and more preferably less than 80 mω.cm²where the several components of the fuel cell are contacted with oneanother under compressive force. Additionally, under compressive force,any protrusions or sharp edges from the fuel cell components, such asthe lands 48 of the separator plates, e.g., 32,34, have the potential todamage the MEA 10. One aspect of the microporous distribution medialayer 17 is that it is constructed of a pliable, compressible, andcompliant material, such that it protects the MEA 10 from any potentialdamage and as such, prolongs the lifespan of the fragile MEA 10 byabsorbing and distributing any pressure points, while serving as thereactant fluid distribution media 17.

Further, in certain embodiments of the present invention, electricallyconductive substrate elements 32,34 do not require the removal of apassivation layer (i.e. metal oxide layer) from the metallic separatorplate substrates 32,34 along contact surfaces 38,40 prior to theirincorporation into the fuel cell assemblies (for example, 9, 11, 101) ofthe present invention. Generally, a metal substrate 32,34 having anoxide layer that contacts a non-metallic fluid distribution layer(without metallized regions 90) creates an impermissibly high electricalcontact resistance. Thus, prior art methods of removing the oxide layerinclude a variety of methods, such as cathodic electrolytic cleaning,mechanical abrasion, cleaning the substrate with alkaline cleaners, andetching with acidic solvents or pickle liquors. Eliminating thenecessity for removing the metal oxides from the contact surfaces 38,40of the metallic separator plate 32,34 is thus optional in accordancewith certain embodiments of the present invention.

In one embodiment of the present invention, the separator elementsubstrates 32,34 comprise stainless steel and the substrate surfaces32,34 do not require extensive removal of a passivation layer from thecontact surface 38,40, such as disclosed in commonly assigned U.S.patent application Ser. No. 10/704,015 filed on Nov. 7, 2003 andincorporated herein in its entirety. The improved electricalconductivity at the interface at the contact regions 44 provided by themetallized region coating 90 on the microporous media 17 permits use ofmetals in the separator element substrates 32,34 that have a naturallyoccurring oxide layer at the contact surface 38,40. Hence, the presentinvention eliminates or significantly simplifies the costly and timeintensive pre-processing step of removing some or substantially all ofthe metal oxides from the contact surface 38,40 of the metal substrates32,34. Further, higher grades of stainless steel previously discussedhave a high corrosion resistance, and thus can be used without anyfurther protective treatment due to their ability to withstand thecorrosive environment within the fuel cell. In certain embodiments ofthe present invention, it is preferred that the contact surfaces 38,40of the separator element metal substrates 32,34 are essentially clean,where loosely adhered contaminants are removed by any method known toone of skill in the art, prior to incorporation into the fuel cellassembly.

In alternate embodiments, the separator plate element substrates 32,34are coated with electrically conductive protective coatings that providecorrosion resistance to the underlying metal substrate 32,34. Suchcoatings may comprise oxidation and corrosion resistant metal coating 90layers (e.g. Au, Ag, Pt, Pd, Ru, Rh, Ir, Os, and mixtures thereof) orcorrosion resistant electrically conductive polymeric matrices, whichgenerally comprise oxidation resistant polymers dispersed in a matrix ofelectrically conductive corrosion resistant particles, as are known inthe art. The protective coatings preferably have a resistivity less thanabout 50 Ohm.cm (Ω.cm). In such an embodiment, where the surfaces 38,40are overlaid with a protective coating, the metal substrates 32,34comprise a corrosion-susceptible metal such as aluminum, titanium, orlower grade stainless steel that is coated with a corrosion resistantprotective coating.

In another embodiment, the present invention provides a method ofoperating a fuel cell comprising positioning an electrically conductivefiberless microporous distribution media layer between a membraneelectrode assembly (MEA) and an electrically conductive substrate. Themicroporous media has a first surface confronting the MEA and a secondsurface confronting the conductive substrate. One or more regions of thefirst surface contact the MEA and likewise, the second surface has oneor more regions that contact the adjacent substrate to form anelectrically conductive path from the substrate through the microporousmedia to the MEA. Electrons are conducted to or from the MEA via thepath while operating the fuel cell.

A reactant stream is introduced to a cathode side of the MEA whileoperating the fuel cell. The reactant stream is delivered through theconductive microporous media and does not require externalhumidification in certain embodiments. In such embodiments, the reactantstream delivered to a cathode side of the MEA consists essentially ofambient air, and the ambient air is not intentionally humidified, or inthe alternative the ambient air has a relative humidity of less thanambient conditions.

In alternate preferred embodiments, the reactant stream introduced tothe cathode side of the MEA for the reaction is externally humidifiedprior to entry into the MEA at less than saturation conditions. Thereactant stream introduced to a cathode side of the MEA has a watercontent of less than a saturation level. In alternate preferredembodiments, the second surface of the microporous media furthercomprises one or more metallized regions comprising an electricallyconductive metal for reducing electrical resistivity between thesubstrate and the microporous media. As appreciated by one of skill inthe art, the microporous media according to the present invention may bearranged on both sides of the MEA.

In some prior art embodiments, coating the metal substrate of thebipolar plates, in particular stainless steel substrates, with aprotective metal coating has created high MEA contamination, which canlead to poisoning of the catalyst (and hence catalyst inactivation) oroverall deactivation of the proton conductive material in the membraneand electrodes over the lifespan of the fuel cell. However, inembodiments where the stainless steel forms a passivation layer of metaloxides, such contamination does not generally occur. Thus, an additionaladvantage of the present invention, is the optional use of an untreatedstainless steel separator plate that forms a protective metal oxidelayer, which reduces MEA contamination, and thus reduces the potentialof catalyst poisoning and overall inactivation of the membrane andelectrodes.

EXAMPLE 1

Experimental details regarding one preferred embodiment of the presentinvention will now be described in detail. As previously described,CARBEL mp30z is a microporous fiberless carbonized ePTFE having 70% byvolume pores, an uncompressed thickness of about 2.5 mils, and iscommercially available from the W. L. Gore Company. In the experiment,gold is deposited by ion-asssisted PVD onto the CARBEL by a Teermagnetron sputter system. The CARBEL media is introduced into the vacuumchamber and when the pressure in the vacuum chamber reaches 5×10⁻⁵ thedeposition of Au is commenced. The magnetron targets are 99.99% pure Au.The Au deposition is done at −50V bias potential using 0.25 A currentfor one minute to achieve a gold coating thickness of 10 nm. Au isdeposited at a rate of 0.16 nm/s using magnetron sputter system. Thethickness of the samples is calibrated using electron probemicroanalysis (EPMA). The deposition temperature is preferably about 25°C. to about 30° C.

EXAMPLE 2

In an alternate method of deposition by electron beam evaporation, theCARBEL mp30z media material, as described above, is introduced into theload lock of an ultrahigh vacuum electron-beam evaporation chamber.After the load lock pressure reaches 10⁻⁷ torr, the sample istransferred to the main deposition chamber. The base pressure of thechamber is 5×10⁻⁹ torr. Au is deposited at a rate of approximately 0.05nm/s using electron-beam evaporation. The rate of deposition iscontrolled by a quartz crystal microbalance and is calibrated usingEPMA. The deposition temperature is preferably about 25 to about 30° C.The quantity of Au deposited can be verified by placing atomically flatsingle crystal pieces of silicon and simultaneously depositing Au on thesilicon and verifying the quantity using the EPMA.

In FIG. 5, Samples were tested on a 50 cm² LANL hadware using a Teledynetest stand. Testing was conducted at different cathode inlet relativehumidity levels to demonstrate the improved water management aspects ofthe present invention. The fuel cell assembly used was arranged to havea Gore MEA 5510 with 0.4 mg/cm² loading of Pt catalyst and a 25 μmthickness was sandwiched between CARBEL mp30z microporous fiberlessdistribution media layers treated in accordance with Example 2 above.The gold was deposited on both an interior and an exterior surface whichare bounded by and in contact with an untreated 316L stainless steelimpermeable substrate. The fuel cell was operated with the followingconditions: 25 psig (approximately 175 kPa), hydrogen to airstoichiometric ratio of 2/2. In all operating scenarios, the fuel celloperating temperature was about 80° C. The fuel cell ran for 24 hours ata constant current density of 1 A/cm². Polarization curves were takenafter activation with different levels of humidification. The cathodeinlet relative humidity (RH) was varied in the following amounts:approximately 50% and 100%. The anode inlet relative humidity waslikewise modified to 50% and 100% relative humidity.

The 50% RH cathode inlet/50% RH anode inlet demonstrated an improvedperformance over the 100% RH cathode inlet/100% RH anode inlet. Animprovement of 20 to 50 mV was observed by decreasing the relativehumidity from 100%/100% to 50%/50%, while cell resistance was similar.Thus, according to the present invention, the membrane is operated underfavorable saturation conditions on the cathode side, while little to noadditional external humidification is necessary.

Fuel cell assemblies prepared in accordance with the present inventionare highly efficient and have enhanced performance. Conductive fiberlessmicroporous fluid distribution media according to the present inventionimproves fuel cell water management by eliminating the need for externalhumidification of the cathode inlet stream while maintaining adequatehydration of the membrane in the MEA leading to a prolonged MEAlifespan.

The present invention also provides an improved electrical interfacebetween the non-metallic microporous fluid distribution media and theelectrodes of the MEA, which reduces electrical resistance and increasescatalyst activity. Such increased catalyst activity can reduce thecatalyst loading requirements in the electrodes of the MEA and thusreduce manufacturing expenses. Further, alternate preferred embodimentsof the present invention likewise reduce the electrical resistancebetween the non-metallic microporous fluid distribution media and themetallic substrate of the separator element, to provide an overall lowerelectrical resistance across the fuel cell. The metallized regions ofthe present invention provide an ultra-thin conductive metal coatingthat sufficiently covers the surface of the microporous fluiddistribution element to provide a low contact resistance for anelectrically conductive fluid distribution element, which improves theoverall performance of a fuel cell. Furthermore, the thickness of themetal coating is such that the manufacturing cost of preparing anelectrically conductive fluid distribution element is minimized.

Processing costs are further reduced by eliminating the step of removingmetal oxides from metal substrates that will form an electricalinterface with the fluid distribution element. The improved electricalinterface reduces contact resistance and promotes more widespread andeven current distribution, which will increase the operationalefficiency and overall lifetime of the membrane and the fuel cell stack.Furthermore, the present invention also enables the traditionaldistribution media layers (fiber-based) to be omitted from the fuel cellassembly architecture, which can promote fuel cell durability andlongevity, as well as cost reductions in fuel cell fabrication costs.

The description of the above embodiments and method is merely exemplaryin nature and, thus, variations that do not depart from the gist of theinvention are intended to be within the scope of the invention. Suchvariations are not to be regarded as a departure from the spirit andscope of the invention.

1. A fluid distribution element for a fuel cell having a membraneelectrode assembly (MEA), the element comprising: a layer comprisingelectrically conductive fiberless microporous distribution media andhaving one or more metallized regions on a surface of said layer, saidone or more metallized regions contacting a major surface of the MEA andforming respective electrically conductive paths between the MEA andsaid media.
 2. The element of claim 1, wherein said fiberlessmicroporous distribution media is substantially free of at least oneelongated particle having an evident long axis including fibers,fibrils, and filaments.
 3. The element of claim 1, wherein said surfaceof said media layer is a first surface and said media layer furthercomprises a second surface opposite to said first surface, wherein saidsecond surface has one or more metallized regions and faces anelectrically conductive impermeable separator plate that is arranged incontact therewith to form one or more electrically conductive pathways.4. The element of claim 3, wherein said separator plate has regions ofmetal oxides formed along contact regions of a separator plate surface,wherein said contact regions correspond to said one or more electricallyconductive pathways.
 5. The element of claim 3, wherein said separatorplate has a surface facing said media layer which is patterned with aplurality of grooves and lands, and wherein said lands are in contactwith said one or more metallized regions of said second surface of saidmedia layer.
 6. The element of claim 5, wherein said media layer iscompliant and compressible and conforms to said lands and grooves tominimize deformation of the MEA when compressive force is applied acrosssaid separator plate through said layer to the MEA.
 7. The element ofclaim 1, wherein each of said metallized regions provides a reducedelectrical resistivity through said respective electrically conductivepaths as compared to a comparative non-metallized layer of microporousmedia.
 8. The element of claim 1, wherein said one or more metallizedregions have an ultra-thin thickness less than about 10 nm.
 9. Theelement of claim 1, wherein said electrically conductive metal isdeposited on surfaces of pores of said microporous media in saidmetallized regions.
 10. The element of claim 1, wherein said microporousmedia comprises a carbonized expanded-polytetrafluoroethylene (ePTFE).11. The element of claim 1, wherein said metallized regions comprise oneor more metals including Ru, Rh, Pd, Ag, Ir, Pt, Os, Ti, Cr, Sn, and Au.12. The element of claim 1, wherein said electrically conductive metalcomprises Au.
 13. A method of operating a fuel cell comprising:positioning an electrically conductive fiberless microporousdistribution media between a membrane electrode assembly (MEA) and anelectrically conductive substrate, wherein said microporous media has afirst surface confronting said MEA and a second surface confronting saidconductive substrate; contacting one or more regions of said firstsurface with said MEA and one or more regions of said second surfacewith said substrate to form an electrically conductive path from saidsubstrate through said microporous media to said MEA; and conductingelectrons to or from said MEA via said path while operating the fuelcell.
 14. The method of claim 13, wherein said contacting isaccomplished by compressive force imparted on the fuel cell in anassembled fuel cell stack.
 15. The method of claim 13, wherein a surfaceof said conductive substrate facing said media is patterned with aplurality of grooves and lands, and wherein said contacting places saidlands in contact with said one or more regions of said second surface ofsaid media.
 16. The method of claim 15, wherein said distribution mediais compliant and compressible, and after said contacting, saiddistribution media conforms to said lands and thereby minimizespermanent deformation of said MEA.
 17. The method of claim 13, whereinat least one of said one or more regions of said first surface or ofsaid second surface are ultra-thin metallized regions comprising anelectrically conductive metal.
 18. The method of claim 17, wherein saidat least one or more regions comprises both of said one or more regionsof said first surface and said one or more regions of said secondsurface.
 19. The method of claim 13, wherein a reactant stream deliveredto said MEA is not humidified or has a relative humidity of less thanambient.
 20. The method of claim 13, wherein said fiberless microporousdistribution media is substantially free of at least one elongatedparticle having an evident long axis including fibers, fibrils, andfilaments.
 21. A method for manufacturing an assembly for a fuel cell,comprising: depositing an electrically conductive metal on a surface ofan electrically conductive fiberless microporous media to form one ormore metallized regions having an ultra-thin thickness, wherein saidmicroporous media comprises carbonized expanded-polytetrafluroethylene(ePTFE); positioning said surface having said metallized regionsadjacent to an electrode of a membrane electrode assembly (MEA); andcontacting said electrode with said surface having said metallizedregions to form an electrically conductive path between said substrateand said microporous media.
 22. The method of claim 21, wherein saiddepositing is conducted by at least one process including electron beamevaporation, magnetron sputtering, plasma-assisted physical vapordeposition, electrolytic deposition, and electroless deposition.
 23. Themethod of claim 21, wherein said electrically conductive metal is one ormore metals including Ru, Rh, Pd, Ag, Ir, Pt, Os, Ti, Cr, Sn, and Au.24. The method of claim 21, wherein said electrically conductive metalcomprises Au.
 25. The method of claim 21, wherein said depositing isconducted to provide said ultra-thin thickness of less than or equal to15 nm.
 26. The method of claim 21, wherein said contacting isaccomplished by compressive force imparted on the fuel cell in anassembled fuel cell stack.